The present invention relates to a baking apparatus and a baking method for baking a resist film coated on a substrate such as a semiconductor wafer and an LCD substrate.
When a semiconductor device is manufactured, photolithgraphic technique is usually employed. In the manufacturing step using the photolithgraphic technique, the surface of a semiconductor wafer is coated with a photoresist, exposed to light together with a predetermined pattern, and developed. In this manner, a resist film having a predetermined pattern is formed on the wafer. If the resist film is further subjected to etching and film-formation steps, a circuit with a predetermined pattern can be formed. The aforementioned series of resist processing steps are usually performed in the coating/developing system, for example, disclosed in U.S. Pat. No. 5,664,254 publication. The series of resist processing steps include various baking processes performed for different purposes. Prebake is made to stabilize the resist. Post exposure bake (PEB) is carried out after the resist is exposed to light. After the resist is developed, post bake is performed.
With an increase in bit number from 64M to 256 M in recent years, the line width of a DRAM circuit has been reduced to the sub micron order, e.g., 0.3 .mu.m or less. With this tendency, the requirement for the quality of a resist film has become extremely stringent. To form such an ultra-fine pattern, highly sensitive, chemically amplified resists have been developed and put in wide use.
Since the light exposed portion of the chemically amplified resists initiates a chemical reaction in a post exposure baking step performed after the light exposure. Therefore, an ultra-fine pattern can be formed even by the radiation of a low energy laser such as a krypton fluoride eximer laser (wavelength: 248 nm). However, when the chemically amplified resist is subjected to the PEB using a conventional baking apparatus, it tends to be difficult to obtain the wiring with a constant width. As a result, a predetermined pattern cannot be formed and thus the yield of the semiconductor device decreases.